FLIGHT TEST: Emivest SJ30 - Long-range rocket

12 October, 2009

SOURCE: Flight International

BY: Mike Gerzanics

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The SJ30 owes it origins to Ed Swearingen, designer of the Metroliner twin-engined turboprop. His studies for a long-range, high-speed light business jet culminated in the concept aircraft flying in 1991. In 1995 a joint company, Sino Swearingen Aircraft, was formed between Swearingen Aircraft and the Taiwan government.

Fresh infusion of capital allowed for a major redesign of the concept aircraft, with the prototype SJ30 growing in all dimensions: it became 1.52m (5ft) longer, 0.31m higher and with a 1.83m greater wingspan. The SJ30 was announced at the 1995 NBAA convention, with the Williams FJ44-1A powered proto­type flying in November 1996.

In September 1997 a production-standard FJ44-2A-powered aircraft was flown. US Federal Aviation Administration type certification was issued in October 2005, with the first customer aircraft delivered in the following October.

Ownership of the SJ30 again changed hands in 2008 when Dubai-based Emirate Investment Development purchased 80% of Sino Swearingen and renamed it Emivest Aerospace. The length of the SJ30's development cycle, from inception to first delivery, spans nearly two decades and has come to rival that of many military procurement programmes. As Emivest was busy with preparations for gaining full production certification, Flight International was invited to fly its unique light business jet.

DESIGN FEATURES

The SJ30 is conventional in construction, with aluminium wings and fuselage with a sprinkling of composites. It is, however, designed for speed. The robust main landing gear retracts into the fuselage, allowing the wing to have a low thickness ratio (maximum aerofoil thickness divided by its chord).

One need only reflect upon the Lockheed F-104's razor-like wing to see the speed advantage that "thinness" brings. At 30°, the SJ30's wing is swept more than two other FJ44-2A powered light jets, the Beechcraft Premier I and Cessna CJ2, at 7° and 0° respectively. Based on historical trends, according to Daniel Raymer in his book Aircraft Design: A Conceptual Approach, a 30° sweep implies speeds in the Mach 0.8 region, at which the SJ30 cruises comfortably.

The other unique aspect of the SJ30's design is its fuel capacity. In general, the more fuel an aircraft carries as a portion of weight, the greater its range. At one extreme is the Virgin Atlantic Global Flyer, powered by a single FJ44 and with a fuel fraction (fuel weight divided by total weight) of nearly 82%. The Global Flyer is able to circumnavigate the globe on a single tank of fuel.

Based on maximum take-off weight, the SJ30 has a fuel fraction of just over 34%. The similarly sized and powered Premier I's fuel fraction is about 29%. With full fuel, the SJ30 can carry 250kg (550lb) of payload (to include the pilot) over 4,635km (2,500nm), while the fully fuelled Premier I can only carry 138kg of payload a distance of 2,520km.

SLATTED WING

How does the SJ30 deliver superior range to the Premier I far in excess of that implied by its larger fuel fraction? Aircraft design, like any engineering endeavour, is a series of trade-offs. An aircraft's wing must be optimised for two differing flight regimes - take-off/landing and cruise. Thick, highly cambered wings give great runway performance, but are a detriment to high-speed cruise performance.

Trailing-edge flaps and leading-edge slats are two common devices used to optimise wing shape for these different flight regimes. While most aircraft feature trailing-edge flaps, leading-edge slats are less common.

In the light-jet arena, the SJ30 is the only aircraft that has a slatted wing, allowing for optimised runway and cruise performance. While the SJ30 can go further and faster than the Premier I, its slatted wing is more costly and complex than its rival's.

The SJ30's wing area of almost 17.8m2 (190ft2), made practical by slats and flaps, is much smaller than the lighter Premier I's area of just under 23m2.

The SJ30 also has a higher aspect ratio wing than does the Premier I. In general, as the aspect ratio of a wing increases, assuming constant wing area, drag decreases for a given amount of lift. The SJ30's highly loaded wing is optimised for high-speed flight, where its thrust-limited speed is faster than the Premier I's, while retaining good field performance.

Conceived in the late 1980s, the SJ30's cabin has an interior floor to ceiling height of 1.3m, identical to a Bombardier Lear 35A's, and sidewall width of 1.4m - 6.1cm (2.4in) narrower than the Learjet.

By contemporary standards, however, it is small. A CJ2's cabin is larger in height (1.46m) and width (1.49m). The class-leading Premier I outshines them both with a cabin height of 1.65m and width of 1.68m. One advantage the SJ30 has over its two rivals is a flat floor - the CJ2 and Premier I both have a sunken aisle.

While its tube may be on the small size, the cabin is sumptuously appointed, with leather seating for four in a club arrangement. The aft seats are larger than the two aft-facing forward seats and recline fully to provide two large berths. The main passenger compartment is separated from the large forward entry area by a hard sliding panel partition.

The foyer has a small storage area (22.7kg) as well as a belted lavatory, allowing for seven occupants. Where the SJ30 soars above the competition is its long legs. With two passengers and a pilot, the SJ30 can fly 4,630km with a 185km alternate and instrument flight rule reserves. With four passengers and the same conditions, the SJ30 can fly 4,110km, more than double the Premier I's 2,030km.

With three occupants and zero wind, the SJ30 can fly across the Atlantic without stopping for fuel in Greenland or Iceland. This same range capability allows it to fly from any point to any other point in the lower 48 US states, while cruising at 436kt (807km/h).

Lightly loaded, the SJ30 has the range and speed of many midsized jets, with substantially lower acquisition and operating costs.

SAN ANTONIO TAKE-OFF

The demonstration flight was from San Antonio International airport, home of Emivest's main assembly plant. Wing and several fuselage components are manufactured in Martinsburg, West Virginia, while the aft fuselage is made in Utah. All components are shipped to San Antonio for final assembly.

Emivest is in the process of revamping its production process to streamline operations. Output of an entire "stuffed" fuselage is about to be moved to Utah, allowing West Virginia to concentrate on the wing. The wing is now shipped in three pieces, making its final assembly and attachment to the fuselage a time-consuming and expensive process. In the long term, Emivest plans to complete the wing in West Virginia and ship the single piece to San Antonio for simplified final assembly.

The preview aircraft, N30SJ, was the first customer aircraft (serial number 6). The concept aircraft was serial number 1, with numbers 2 through 5 taking part in the development effort. N30SJ was production representative and had about 850 flight hours on it.

My safety pilot was Paul Arrambide, who previously had flown N30SJ for the launch customer. The pre-flight safety inspection yielded few surprises save the ventral strake and its rudder. The pilot's rudder pedals are connected to the conventional rudder on the vertical stabiliser for normal flight control inputs. The ventral rudder, which has about one-third of the rudder's authority, is used for other functions and does not move the rudder pedals. Dual full-time yaw dampers and the autopilot actuate only the ventral rudder.

Like the Premier I, the SJ30 has a rudder bias system designed to reduce pilot workload in the event of an engine failure. The bias system senses an asymmetric power condition based on differential engine bleed air pressure. Unlike the several aircraft I have flown with rudder bias systems, the SJ30's only moves the lower ventral rudder.

Also of note during the walk around was the aft baggage compartment, accessible through a 44.5 x 54.6cm door below the left engine nacelle. The 1.5m3 (53ft3) compartment is rated for 227kg of baggage.

Entrance is through an 81.3 x 118cm air-stair door that incorporates four steps and has a passive and pneumatic seal. Hard sliding panels separate the cockpit from the foyer area.

I found the cockpit to be as roomy as the midsized Piaggio P180 Avanti. Flight instrumentation is anchored by a Honeywell Primus Epic CDC system with three 8 x 10in LCD displays. Overall, the cockpit is well arranged, with system control panels along the bottom edge of the forward instrument panel.

While well equipped, a second flight management system with a second GPS navigation system may be a popular option. For those contemplating using the SJ30's transatlantic range, an HF radio is available.

Pre-start procedures were easily accomplished, with a paper checklist used to ensure their completion. An external power cart was connected for the pre-start operations, allowing the vapour cycle air conditioner to cool the aircraft on a 30°C (86°F) Texas day.

In preparation for engine start, the cart was disconnected and both FJ44-2A engines started off the aircraft battery. I kept an eye on each engine's inter-turbine temperature during the start, which peak well below the 1,000°C limit. Each engine produces 2,300lb (10.2kN) of thrust and is flat rated to ISA+7°C.

The FJ44s do not have full authority digital engine control, they are controlled by an electronic fuel controller (ECU) with dedicated hydromechanical back-up. The throttle quadrant had three detents above cut-off: idle, MCT and TO. Placing the thrust levers in these detents allows the ECU to automatically keep thrust at an optimal setting. Advancing the thrust to about 40% N1 from its idle of 29% N1 started the aircraft rolling.

I found the pedal-controlled nosewheel steering to be fairly linear and allowed for accurate tracking of taxiway centrelines. For tight turns a button on the left-hand side console increases nosewheel steering authority from +/-10° to +/-60°.

The toe-actuated main wheel brakes have two anti-skid channels that allowed me to keep taxi speed to a moderate pace en route to Runway 21. Flaps were set to 10° and computed V speeds input into the flight management system. Performance data can be derived from paper look-up tables or from an optional laptop-based planner.

Once on the runway and cleared for take-off, I released the brakes and rapidly moved the thrust levers into the TO detent. The ECUs stabilised the engines at 102% N1, and the SJ30 accelerated briskly. At an indicated airspeed of 97kt, Arrambide called "V1" followed by "rotate" at 103kt. With two occupants and 1,340kg of fuel, the 5,460kg aircraft lifted off the runway after a 610m ground roll.

At maximum take-off weight and standard conditions, Emivest publishes a total take-off distance of 1,217m, including climbing over a 35ft obstacle. In a 12° nose high pitch attitude the jet stabilised at a trim speed of 136kt.

At an acceleration height of 1,000ft above ground level the nose was lowered, passing 160ft the flaps were retracted and acceleration continued until an initial climb speed of 250kt was captured. Five minutes after starting the take-off roll the thrust levers were retarded to the MCT detent for the climb to altitude.

DIRECT CLIMB

At maximum take-off weight on a standard day, the SJ30 can climb directly to FL430, and at our test day take-off weight, Emivest data shows that it could climb directly to FL450. We decided to only climb to FL430. During the climb I was able to get a feel for the SJ30's controls with a series of gentle 30° angle of bank turns at an indicated airspeed of 250kt.

During the development programme one modification to the conventional ailerons was to increase the thickness of their trailing edge to increase lateral stability and control at high speeds. I found roll control forces to be fairly low and linear with no rudder input required to co-ordinate the turns.

Passing FL320 an indicated Mach of 0.70 was held until levelling off at FL430. Time from brake release to level off was roughly 24min, with a total of fuel burn of 263kg, numbers matching Emivest's published data.

Thrust was kept at the MCT detent, which gave an N1 of 104.3%. After several minutes the SJ30's speed stabilised at M0.812 with an indicated airspeed of 230kt. Total fuel flow at a true airspeed of 459kt was 386kg/h (850lb/h), at nearly standard day conditions. These high-speed cruise numbers match well with Emivest's data and highlight its speed advantage over comparable light jets.

Next, the thrust levers were retarded to around 99% N1 to spot-check long-range cruise performance. With a target Mach of 0.76 desired, I found the speed trend arrow in the primary flight display helpful in stabilising at the long-range cruise speed of 213kt. At M0.76 the true airspeed was 430kt, with a total fuel flow of only 327kg/h.

SEA LEVEL CABIN

With the autopilot engaged, I left the aircraft in the able hands of Arrambide to sample the passenger cabin. With the aft partition doors closed, I found the ambient noise level to be on a par with other light business jets I had flown. While not objectionable, I discerned some fan noise while seated in the aft berthing seats.

Emivest is altering some duct work to alleviate this source of noise. One unique aspect of the SJ30 is its pressurisation system. While most aircraft cabin pressurisation systems run at delta pressures of about 0.55-0.62bar (8-9lb/in2), the SJ30's operates at 0.83bar, which gives a sea level cabin up to FL410.

On test day at FL430 the indicated cabin altitude was only 500ft, whereas the typical business jet would have a cabin altitude of about 6,000ft. The practical effect of a sea-level cabin is that travel is less fatiguing, allowing passengers to arrive more refreshed.

Once back in the saddle, I performed several 45° angle-of-bank steep turns at FL430 and M0.76. Roll and pitch forces were well harmonised and no buffet was felt during the manoeuvring. The power was left up and a descent initiated to investigate the SJ30's high-speed flight characteristics.

As MMO was approached, the airspeed tape on the display changed to alert the pilot to an impending overspeed. Passing MMO, M0.83, an aural warning sounded. Stabilised at M0.83, a series of half amplitude control inputs showed the SJ30's response in all three control axes to be well damped. Pulling the power back and extending the speed brakes caused a noticeable nose pitch-up, a helpful trait when trying to back out of an overspeed situation.

This helpful characteristic was not always present in the SJ30. Initially, the wing-mounted speed brakes were placed inboard of their current production position. Extension of the pre-production speed brakes caused the horizontal tail to be partially blanked out, with a resultant nose-down pitch moment at the worst possible time. The descent was stopped at FL310 where a final cruise point was evaluated.

With the power set in the MCT detent, total fuel flow was 599kg/h and the SJ30 held M0.817. At a static air temperature of -34°C, the SJ30 was zipping along at a true airspeed of 494kt. The SJ30 is hands down the fastest light jet I have flown.

After quenching my thirst for speed, the descent was continued down to 15,000ft mean sea level, where I briefly evaluated the SJ30's slow speed handling qualities.

STALLS AND FALLS

The first approach to stall was in a clean configuration. The power was set to 50% N1 and level flight held to allow the SJ30 to slow. At a gross weight of 4,935kg, the stick shaker went off at an indicated airspeed of 129kt. Had I ignored the shaker, the stick pusher would have fired to force the nose of the aircraft down and break the stall. Recovery at shaker onset was effected by rapidly advancing the power to the TO detent, the ECU preventing any exceedences, and reducing yoke back pressure. As the airspeed increased, the flaps were set to 10° to increase the stall margin.

From a technical standpoint, lowering the flaps would increase the stall margin, but in my several years of aviation experience this was the first jet aircraft where changing aircraft configuration in a critical phase of flight was a recommended procedure.

The next approaches to stall were in the TO - flaps 10° and gear up - and landing - flaps 31° and gear down - configurations. With the power again set provide a slow airspeed bleed-off for stall entry, shaker activation speeds were at indicated airspeeds of 102kt and 92kt respectively.

Recovery to normal flight conditions was again effected by rapidly advancing the power to the TO detent and relaxing yoke back pressure. In the TO configuration approach to stall, no configuration changes were made during the recovery manoeuvre. For the recovery in the landing configuration, the flaps were retracted to 10° after the stall was broken.

While this procedure may provide for an optimal recovery when executed correctly, inadvertent retraction of the flaps to the full-up position during this critical phase of flight could place the aircraft in an even more adverse condition than one that prompted the recovery. During a stall recovery the pilot should be allowed to focus his attention on flying the aircraft, not changing configuration in search of the perfect recovery.

STALL RECOVERY

Regardless of the recovery technique used, the SJ30 displayed no tendency to drop a wing at shaker onset speeds. In all configurations at shaker onset speed, the SJ30 was responsive to control inputs in all three control axes.

While hand flying the SJ30 for the return to San Antonio, I extending the speed brakes at indicated airspeeds ranging from 200kt to 250kt. In all cases they proved effective at slowing the aircraft with some noticeable burble and little or no nose-up pitching tendency.

While a nose-up pitching moment is a good trait at speeds approaching VMO/MMO, at pattern airspeeds it is not, and the extensive development process has paid dividends for Emivest and the SJ30. I found the SJ30 a delight to hand fly, with pitch and roll control forces well harmonised.

The first approach was a visual straight in to Runway 21. Pitch force changes during gear and flap extension were minimal, with pitch trim readily nulling out any remaining yoke forces. Runway 21 lacks a precision approach and I used the visual approach slope indicator to fly the glidepath. With flaps set to 20°, approximately 68% N1 was required to fly an approach indicated airspeed of 109kt (VREF +5kt) for the 4,831kg aircraft. When landing was assured the flaps were set to 31°/full.

The power was retarded to idle at about 40ft above ground level, with a minor flare initiated about 10ft above the runway. The SJ30's trailing link landing gear ensured a smooth touchdown about 400m down the runway.

Once on the runway, the speed brakes were manually extended with moderate wheel braking bringing the aircraft to a halt less than 1,150m from the approach threshold. At a gross weight of 4,570kg and standard conditions, Emivest lists a landing distance of 778m, which assumes crossing the threshold at 50ft.

Once clear of the runway, we taxied back for the final take-off and landing. V speeds were slightly lower than the initial take-off, the flaps again set to 10°. The only difference between this and the first take-off would be Arrambide pulling the right engine to idle just after calling V1 at an indicated airspeed of 95kt.

Less than 20kg of left pedal was needed to keep the aircraft tracking down the runway, the rudder bias system significantly reducing required pedal forces. Once lateral control was assured I rotated the aircraft, lifting off at about 110kt, slightly above the V2 speed of 107kt.

A climb speed of 115kt was held until reaching an engine-out acceleration altitude of 400ft above ground level. During the climb roughly half of the available rudder trim reduced pedal forces to zero. A visual circuit was again flown to Runway 21. Flaps again were set to 20°, and 80% N1 on the left engine was required to hold a target indicated airspeed of 120kt. While the flight manual target speed was 109kt, the long runway and visual conditions allowed the higher speed to be safely flown.

Compared with the first approach, the faster speed held on the single-engine approach felt more comfortable and stable. Power on the good engine was reduced to idle passing 50ft above ground level and a soft touchdown again was ensured by the trailing link landing gear. Moderate wheel braking again brought the SJ30 to a halt 1,150m down the runway.

Taxi back to Emivest's ramp for engine shutdown again highlighted the SJ30's good nosewheel steering system. Post-flight flows were straightforward and rapidly accomplished. During my 2h flight I was convinced that from performance and flying qualities standpoints Emivest has a winner on its hands.

NICHE OF ITS OWN

The SJ30's ability to cruise at speeds approaching M0.80 and its 4,630km range when lightly loaded make it a long-range rocket in a niche of its own. The cabin is small when compared with the Premier I, but 250 orders show many are willing to trade space for time.

Operational support is an essential element of a business jet purchase. Emivest says it is committed to providing a first-class support network for the SJ30 and once a viable support structure is in place, the SJ30 will not have to sell itself on its merits alone.